1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and a method of manufacturing the same, and more particularly to a semiconductor pressure sensor including polysilicon gauge resistors and a method of manufacturing the same.
2. Description of the Background Art
As a type of pressure sensor, a semiconductor pressure sensor using a semiconductor substrate is used. In such a semiconductor pressure sensor, a plurality of diffused resistors serving as gauge resistors of which the resistance varies in accordance with pressure applied thereto are formed on a surface of a silicon substrate and the diffused resistors are bridged by diffusion wires of which the resistance value is low. The gauge resistors are arranged, for example, at respective portions of four sides of a rectangular diaphragm (thin film). On the other hand, on a surface of the silicon substrate which is opposite to the region in which the gauge resistors are arranged, a recess is formed to form a diaphragm therein. Japanese Patent Application Laid Open Gazette No. 3-6824 (Patent Document 1) discloses this type of semiconductor pressure sensor.
In the background-art semiconductor pressure sensor, the above-discussed recess, i.e., the diaphragm is formed by grinding a silicon substrate to a predetermined thickness and then etching a back surface of the silicon substrate with a predetermined etching mask.
In such a manufacturing method, the thickness of the silicon substrate under the recess is controlled by the length of etching time, and this causes a problem that the thickness of the diaphragm is apt to vary. Further, even in an attempt to reduce the thickness of the diaphragm, the thickness can be reduced up to about 10 μm at least in consideration of the variation in the amount of silicon in the substrate surface to be grinded and etched. Furthermore, since the variation in the amount of silicon of the substrate to be etched may cause misalignment between the gauge resistors and the recess, it is difficult to downsize the semiconductor pressure sensor with high accuracy.